A Blog on Science, Medicine, and Education

Point of View

In Dead Poet’s Society, the late Robin Williams urged his students to stand on their desks to look at the world in a different way. This is a fitting message for this week, as November 24, 2015 marks the 156th anniversary of the publication of Darwin’s On the Origin of Species. This book challenged us all to do just that.

Photo credit: Ella Daniels-Koch

Our eyes sometimes trick us.

The sun rises in the morning and sets in the afternoon. From these observations, it’s obvious that the sun moves and the Earth stays still. Yet we all know (now) that it’s the other way around.

Optical illusions tell us the same thing – what we think we see is not always what is literally right in front of us. For example, in the checkerboard below, the squares marked A and B are precisely the same shade of gray.

Square A is the same color as square B. Original image by Edward H. Adelson.

And it’s not just our eyes – sometimes our common sense also misleads us. We all know from everyday experience that time moves at a constant rate, except Einstein taught us that it depends on how fast we are moving. We are certain that heavy objects fall faster than light objects, except that they don’t – they fall at the same rate.

In other words, our senses, even our intuition – the very things that we use to navigate the world – are not always trustworthy.

The same thing can be said of the natural world. Take a look around. Note the plants and animals of our everyday experience. Do they evolve? Apparently not. They just seem to stay the same. An oak tree is an oak tree. A cat is a cat.

But our lifetime is relatively short. Can we go back even farther? Consider old photographs, or ask our grandparents what oak trees and cats looked like in their day. Again, we run up against the same answer – they really haven’t changed at all.

Maybe we need an even longer timeline. How about Renaissance paintings dating back to 15th century, or Medieval sculptures from the 10th century, or ancient Greek writings? Can we find evidence of what organisms looked like back then? We can, and again, the organisms then looked about the same as they do today.

So, our everyday experience tells us something very clear – organisms don’t seem to change in ways we can perceive. It’s natural, even commonsensical, to infer that evolution does not occur.

Photo credit: Ben Morris

But let’s look again. To “see” evolution, we have to change our vantage point, like looking at the Earth from space rather than from the ground. One way to do this is to consider organisms that reproduce much more quickly than oak trees and cats.

Bacteria, for example. Some bacteria divide every 20 minutes. So, in the time it takes for a cat to grow up and reproduce (1 generation), a single bacterium can go through hundreds of thousands of generations. Time hasn’t sped up, but our ability to see change over many generations is much easier.

Do we see bacteria change? The answer is yes. Think about antibiotic resistance. We use antibiotics to kill bacteria, and before we know it, antibiotic resistance is a major public health problem. The population of bacteria changed over time – the bacteria evolved. They went from being antibiotic sensitive to antibiotic resistant. This is evolution in a matter of days or weeks, in a way that makes the slow and invisible fast and visible.

Are there other ways to “see” evolution? Yes, fossils extend our timeline back even before the ancient Greeks. We can find fossils that are a thousand, million, billion, even several billion years old. With such a long timeline, we are able to see wildly different organisms, ones that are even more different than antibiotic resistant and sensitive bacteria, from dinosaurs to ammonites to trilobites, long extinct but once numerous.

Bacteria are small, and fossils are not living. Can we “see” evolution in organisms that are all around us – the plants and animals of our everyday experience? The answer is yes, but it takes careful measurement.

Princeton University biologists Peter and Rosemary Grant saw evolution in action in finches in the Galápagos Islands, where Charles Darwin famously stopped in his five-year journey around the world. By carefully measuring beak sizes in times of drought, when competition for food was intense, they recorded measureable changes in beak size over as little as one generation. Is it still a finch? Yes. But is it evolution? Yes.

Another example of evolution right under our noses comes from Nebraska where again a husband-and-wife team, Charles and Mary Brown, studied cliff swallows. The researchers looked at road kill – birds that were hit by cars – and noticed that the number of birds hit by cars declined over time, and the wing length of birds that were killed was longer than that of the general population. Putting the two observations together, they reasoned that the birds evolved shorter wings over time, making them better able to avoid being hit by oncoming cars.

If change is so hard to see, how did Darwin ever come up with a theory of evolution? The answer is that he was not really trying to understand how organisms change. He was trying to solve another problem – the problem of design.

The problem of design is that organisms look like they were designed for what they do. Think of a Great White Shark. Everything about it tells you it is a hunter: strong, powerful jaws; sharp teeth, a streamlined body, a keen sense of smell, a powerful tail.

Or consider the human eye, with features that remind us of a camera: an aperture (the iris), a lens, and a light-sensitive layer in the back (the retina).

Biologists call these adaptations, and they are all around us. In fact, Darwin and many others before him were fascinated with adaptations. He wrote in the opening pages of the Origin that he set out to determine “how the innumerable species inhabiting this world had been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration.”

The shark and the eye look like they were built in their present form for their present function. It makes perfect sense.

That is, until Darwin came up with a different explanation – the theory of evolution by natural selection. Darwin taught us that small changes, over vast spans of time, lead to features like shark’s teeth or the human eye.

Evolution is, in a way, non-obvious and actually runs counter to our everyday observations. Science can provide a way to see what is not obvious to our senses. What we learn through science is that the world is more complicated than we might otherwise think, even counterintuitive at times.

As Lisa Randall, professor of physics at Harvard, writes in her recent op-ed in The Boston Globe, “The world looks entirely different at the scale of the atom…than it does from your chair or from space. This why the rules of quantum mechanics can appear unintuitive or illogical…People relate best to scales they encounter in their daily lives.”

Thanks! I saw the Lichtenstein house when I was visiting DC with my family last winter. It’s really fun to walk around it and see it change right before your eyes. The video does a good job of capturing these different perspectives.

Great piece! I love being reminded that Darwin’s initial mission was to explain design, as it is a reminder that what he discovered rocked the roots of a theistic culture. In theorizing that organisms evolve over time, he turned the idea of God’s perfectly designed universe on its head. And thanks for the link to Randall’s fascinating op-ed!

Just came across this fitting quote from Levin in Tolstoy’s Anna Karenina: “But I, watching the movement of the stars, cannot picture to myself the rotation of the earth and I am right in saying that the stars move.”